The Female Reproductive Cycle

Two linked cycles, one system. The female reproductive cycle has two coordinated parts: the ovarian cycle (events in the ovary, maturing and releasing an egg) and the uterine cycle (changes in the uterine lining). Both are driven by hormones from the pituitary (FSH, LH) and ovaries (estrogen, progesterone), all working through feedback.

The ovarian cycle. In the ovary, an egg matures and is released:

• Follicular phase: stimulated by FSH, a follicle (containing an egg) grows and produces rising estrogen.
• Ovulation: a surge of LH (triggered by high estrogen) causes the mature egg to be released from the ovary — around the middle of the cycle. This is the fertile window.
• Luteal phase: the leftover follicle becomes the corpus luteum, which secretes progesterone (and estrogen) to prepare the body for possible pregnancy. If no pregnancy occurs, the corpus luteum breaks down, hormone levels fall, and the cycle restarts.

The uterine (menstrual) cycle. In parallel, the uterine lining (endometrium) changes:

• Menstrual phase: if no pregnancy occurred, the thickened lining is shed (menstruation, the "period").
• Proliferative phase: rising estrogen rebuilds and thickens the lining.
• Secretory phase: progesterone (from the corpus luteum) further prepares the lining to receive a fertilized egg.

How the hormones connect them. The two cycles are synchronized by the hormones: FSH grows the follicle → estrogen thickens the lining → LH surge triggers ovulation → corpus luteum's progesterone maintains the lining. If pregnancy occurs, the developing embryo signals the corpus luteum to keep producing progesterone, preserving the lining. If not, falling hormones cause the lining to shed, and the cycle begins again. This is an elegant example of negative and positive feedback timing a repeating biological process.

How it works

The cycle, integrated:

FSH → follicle grows → estrogen ↑ → thickens uterine lining (proliferative)
Estrogen peak → LH surge → OVULATION (egg released)
Corpus luteum → progesterone → maintains lining (secretory)
No pregnancy → hormones fall → lining sheds (menstruation) → cycle restarts
Pregnancy → corpus luteum sustained → lining preserved

Comparisons

Common confusions

• Ovulation is mid-cycle, triggered by the LH surge — the fertile point.
• Ovarian vs uterine cycle. Ovary matures/releases the egg; uterus prepares/sheds the lining — synchronized by hormones.
• Corpus luteum makes progesterone to maintain the lining after ovulation.
• Menstruation happens when hormones fall (no pregnancy), not randomly.

Memory aids

• "FSH grows the Follicle; LH surge = Launch (ovulation)."
• Corpus luteum = "progesterone producer after ovulation."
• Estrogen builds the lining; progesterone maintains it.

Quick review

• The female reproductive cycle links the ovarian cycle (follicular → ovulation at the LH surge → luteal/corpus luteum) with the uterine cycle (menstrual → proliferative → secretory).
• FSH grows the follicle; estrogen thickens the lining; the LH surge triggers ovulation; progesterone (corpus luteum) maintains the lining.
• No pregnancy → hormones fall → lining sheds (menstruation); pregnancy → corpus luteum sustained.
• Underlies contraception, fertility, and cycle disorders like PCOS.